add StringBuilder to improve performance and add ConvertPlaceHolder f…

…unction

builder.go

@@ -4,6 +4,10 @@
 
 package builder
 
+import (
+	"fmt"
+)
+
 type optype byte
 
 const (
@@ -186,6 +190,33 @@ func (b *Builder) ToSQL() (string, []interface{}, error) {
 	return w.writer.String(), w.args, nil
 }
 
+// ConvertPlaceholder replaces ? to $1, $2 ... or :1, :2 ... according prefix
+func ConvertPlaceholder(sql, prefix string) (string, error) {
+	buf := StringBuilder{}
+	var j, start = 0, 0
+	for i := 0; i < len(sql); i++ {
+		if sql[i] == '?' {
+			_, err := buf.WriteString(sql[start:i])
+			if err != nil {
+				return "", err
+			}
+			start = i + 1
+
+			_, err = buf.WriteString(prefix)
+			if err != nil {
+				return "", err
+			}
+
+			j = j + 1
+			_, err = buf.WriteString(fmt.Sprintf("%d", j))
+			if err != nil {
+				return "", err
+			}
+		}
+	}
+	return buf.String(), nil
+}
+
 // ToSQL convert a builder or condtions to SQL and args
 func ToSQL(cond interface{}) (string, []interface{}, error) {
 	switch cond.(type) {

builder_test.go

@@ -460,3 +460,18 @@ func TestExprCond(t *testing.T) {
 	assert.EqualValues(t, "SELECT id FROM table1 WHERE (a=? OR b=?) AND (c=? OR d=?)", sql)
 	assert.EqualValues(t, []interface{}{1, 2, 3, 4}, args)
 }
+
+const placeholderConverterSQL = "SELECT a, b FROM table_a WHERE b_id=(SELECT id FROM table_b WHERE b=?) AND id=? AND c=? AND d=? AND e=? AND f=?"
+const placeholderConvertedSQL = "SELECT a, b FROM table_a WHERE b_id=(SELECT id FROM table_b WHERE b=$1) AND id=$2 AND c=$3 AND d=$4 AND e=$5 AND f=$6"
+
+func TestPlaceholderConverter(t *testing.T) {
+	newSQL, err := ConvertPlaceholder(placeholderConverterSQL, "$")
+	assert.NoError(t, err)
+	assert.EqualValues(t, placeholderConvertedSQL, newSQL)
+}
+
+func BenchmarkPlaceholderConverter(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		ConvertPlaceholder(placeholderConverterSQL, "$")
+	}
+}

cond.go

@@ -5,7 +5,6 @@
 package builder
 
 import (
-	"bytes"
 	"io"
 )
 
@@ -19,15 +18,15 @@ var _ Writer = NewWriter()
 
 // BytesWriter implments Writer and save SQL in bytes.Buffer
 type BytesWriter struct {
-	writer *bytes.Buffer
-	buffer []byte
+	writer *StringBuilder
 	args   []interface{}
 }
 
 // NewWriter creates a new string writer
 func NewWriter() *BytesWriter {
-	w := &BytesWriter{}
-	w.writer = bytes.NewBuffer(w.buffer)
+	w := &BytesWriter{
+		writer: &StringBuilder{},
+	}
 	return w
 }
 

strings_builder.go

@@ -0,0 +1,119 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package builder
+
+import (
+	"unicode/utf8"
+	"unsafe"
+)
+
+// A StringBuilder is used to efficiently build a string using Write methods.
+// It minimizes memory copying. The zero value is ready to use.
+// Do not copy a non-zero Builder.
+type StringBuilder struct {
+	addr *StringBuilder // of receiver, to detect copies by value
+	buf  []byte
+}
+
+// noescape hides a pointer from escape analysis.  noescape is
+// the identity function but escape analysis doesn't think the
+// output depends on the input. noescape is inlined and currently
+// compiles down to zero instructions.
+// USE CAREFULLY!
+// This was copied from the runtime; see issues 23382 and 7921.
+//go:nosplit
+func noescape(p unsafe.Pointer) unsafe.Pointer {
+	x := uintptr(p)
+	return unsafe.Pointer(x ^ 0)
+}
+
+func (b *StringBuilder) copyCheck() {
+	if b.addr == nil {
+		// This hack works around a failing of Go's escape analysis
+		// that was causing b to escape and be heap allocated.
+		// See issue 23382.
+		// TODO: once issue 7921 is fixed, this should be reverted to
+		// just "b.addr = b".
+		b.addr = (*StringBuilder)(noescape(unsafe.Pointer(b)))
+	} else if b.addr != b {
+		panic("strings: illegal use of non-zero Builder copied by value")
+	}
+}
+
+// String returns the accumulated string.
+func (b *StringBuilder) String() string {
+	return *(*string)(unsafe.Pointer(&b.buf))
+}
+
+// Len returns the number of accumulated bytes; b.Len() == len(b.String()).
+func (b *StringBuilder) Len() int { return len(b.buf) }
+
+// Reset resets the Builder to be empty.
+func (b *StringBuilder) Reset() {
+	b.addr = nil
+	b.buf = nil
+}
+
+// grow copies the buffer to a new, larger buffer so that there are at least n
+// bytes of capacity beyond len(b.buf).
+func (b *StringBuilder) grow(n int) {
+	buf := make([]byte, len(b.buf), 2*cap(b.buf)+n)
+	copy(buf, b.buf)
+	b.buf = buf
+}
+
+// Grow grows b's capacity, if necessary, to guarantee space for
+// another n bytes. After Grow(n), at least n bytes can be written to b
+// without another allocation. If n is negative, Grow panics.
+func (b *StringBuilder) Grow(n int) {
+	b.copyCheck()
+	if n < 0 {
+		panic("strings.Builder.Grow: negative count")
+	}
+	if cap(b.buf)-len(b.buf) < n {
+		b.grow(n)
+	}
+}
+
+// Write appends the contents of p to b's buffer.
+// Write always returns len(p), nil.
+func (b *StringBuilder) Write(p []byte) (int, error) {
+	b.copyCheck()
+	b.buf = append(b.buf, p...)
+	return len(p), nil
+}
+
+// WriteByte appends the byte c to b's buffer.
+// The returned error is always nil.
+func (b *StringBuilder) WriteByte(c byte) error {
+	b.copyCheck()
+	b.buf = append(b.buf, c)
+	return nil
+}
+
+// WriteRune appends the UTF-8 encoding of Unicode code point r to b's buffer.
+// It returns the length of r and a nil error.
+func (b *StringBuilder) WriteRune(r rune) (int, error) {
+	b.copyCheck()
+	if r < utf8.RuneSelf {
+		b.buf = append(b.buf, byte(r))
+		return 1, nil
+	}
+	l := len(b.buf)
+	if cap(b.buf)-l < utf8.UTFMax {
+		b.grow(utf8.UTFMax)
+	}
+	n := utf8.EncodeRune(b.buf[l:l+utf8.UTFMax], r)
+	b.buf = b.buf[:l+n]
+	return n, nil
+}
+
+// WriteString appends the contents of s to b's buffer.
+// It returns the length of s and a nil error.
+func (b *StringBuilder) WriteString(s string) (int, error) {
+	b.copyCheck()
+	b.buf = append(b.buf, s...)
+	return len(s), nil
+}